In a hydraulic brake system, a master cylinder device is generally employed for pressurizing a working fluid and supplying the pressurized working fluid to a brake device. For instance, in the master cylinder device disclosed in the following Patent Literature, a pressurizing piston for pressurizing the working fluid to be supplied to the brake device and an input piston to which an operation force by a driver is applied are provided so as to be spaced apart from each other. In general, the operation force is not transmitted to the pressurizing piston. Accordingly, the master cylinder device is configured such that the pressurizing piston moves forward while depending on a pressure of a highly pressurized working fluid supplied thereto, so as to pressurize the working fluid. Further, in the disclosed master cylinder device, where a comparatively large braking force is required, for instance, the input piston comes into contact with the pressurizing piston, and the pressurizing piston moves forward while depending on the operation force, in addition to the pressure of the highly pressurized working fluid, thereby pressurizing the working fluid.